Transparent OLED device with high intensity

ABSTRACT

The present invention relates to an organic light emitting device (OLED) ( 100;200;400;800;900;1000;1100;1200 ) comprising a first substrate layer ( 101;201;401;501;701;1004;1104;1205 ) and a second substrate layer( 102;202; 402;502;704; 1005;1105;1206 ). The device ( 100;200;400;800;900;1000;1100;1200 ) further comprises at least a first OLED assembly ( 103;403;503;901;1001;1101;1202 ) and a second OLED assembly ( 104;404;504;902;1002;1102;1203 ) arranged between the first and the second substrate layers. Each of the first and second OLED assemblies comprises a first electrically conductive layer( 105;505;703 ), a second electrically conductive layer ( 106;506;706 ) and an organic light emitting layer ( 107;507;507′;707 ) arranged between the first and the second electrically conductive layer. The organic light emitting device ( 100;200;400;800;900;1000;1100;1200 ) of the invention allows for an increased light intensity and is suitable for large area applications.

FIELD OF THE INVENTION

The present invention relates to an organic light emitting device(OLED).

TECHNICAL BACKGROUND

Due to their high resolution, high quality images and independence frombacklight sources, organic light emitting devices (OLEDs) have attractedconsiderable attention in display and lighting applications.

An OLED typically comprises an anode layer, a cathode layer and anorganic electroluminescent layer positioned between the anode and thecathode layers. Upon application of an electric potential, light isemitted from the device.

The intensity of light emitted by an individual OLED may be inadequatefor certain applications in which higher intensity emission is required.

In order to improve the intensity of light, and hence the performance ofthe device, individual OLEDs may be arranged in stacks.

Such an arrangement is e.g. disclosed in U.S. Pat. No. 6,693,296,wherein an OLED apparatus comprising a substrate and a plurality of OLEDdevices is disclosed. Each of the plurality of OLED devices includes atleast one organic layer extending over an edge of a corresponding spacedapart bottom electrode.

One problem associated with the OLED apparatus of U.S. Pat. No.6,693,296 is that excess absorption of light may occur within the stackdue to the high absorbance of the electrodes. As a result, the overalllight intensity may be reduced.

Accordingly, there is a need in the art to provide an OLED device whichprovides for an enhanced light intensity of the emitted light,especially for use in large-area applications.

SUMMARY OF THE INVENTION

An object of the present invention is to at least partly overcome theabove-mentioned problems and to address the need in the art.

Especially, it is an object of the present invention to provide anorganic light emitting device which allows for an increased lightintensity.

According to one aspect, the invention relates to an organic lightemitting device (OLED) comprising a first substrate layer and a secondsubstrate layer. The device further comprises at least a first OLEDassembly and a second OLED assembly arranged between the first and thesecond substrate layers. Each of the first and second OLED assembliescomprises a first electrically conductive layer, a second electricallyconductive layer and an organic light emitting layer arranged betweenthe first and the second electrically conductive layer. Each of thefirst and second OLED assemblies is arranged to form a non-zero angle inrelation to at least one of the first and the second substrate layers.

The present invention is based upon the realization that such a deviceallows for a higher density of light emitting structures, and hence animproved light intensity per unit surface area since several OLEDassemblies may be arranged in parallel to form a non-zero angle to thesubstrate layers.

Furthermore, in this arrangement the disadvantages associated withvertically stacked OLEDs are avoided, such as the absorption of lightwithin the stack.

Light emitted from at least one of the OLED assemblies is emitted eitherthrough the first substrate layer or the second substrate layer, orboth. Hence, at least one of the first and the second substrate layersmay be transparent.

Accordingly, light may be emitted from either a single surface of fromseveral surfaces, thereby enhancing the total light intensity of theOLED device. It is also possible to obtain various ratios of lightemission from different surfaces.

Furthermore, the angle between the OLED assemblies and the substrate(s)determines the density of OLED assemblies that can be achieved in theOLED device. The density can be expressed as a ratio between the lengthof the OLED assemblies and the distance between adjacent OLEDassemblies. This ratio may advantageously be greater than 1, and moreadvantageously range between 2 and 5.

Moreover, by selecting a suitably large angle between the substrate andthe OLED-assemblies it is possible to achieve an OLED device combining ahigh output intensity with a high transparency. This makes it possibleto look through the device in the on-state without being blinded by thehigh light intensity. Alternatively, such an arrangement allows lightfrom external sources, such as daylight to enter only under controlleddirections, while being able to emit a controlled amount of light inother controlled directions.

To this end, each of the first and the second OLED assemblies may bearranged to form an angle which is greater than 30° in relation to atleast one of the first and the second substrate layers.

The substrate layers are typically arranged in parallel, and by varyingthe angle between the OLED assemblies and the substrate layers, thedirection of the emitted light may be adjusted. Accordingly, the lightemission can be directed and controlled.

Preferably, each of the first and the second OLED assemblies may bearranged to form an angle of 90° in relation to at least one of thefirst and the second substrate layers.

This allows for an increased light intensity per unit surface area sinceseveral OLED assemblies may be arranged in parallel.

Thus, the light emitting layers of the first and the second OLEDassemblies, respectively, are typically arranged to face each other andlight may be emitted parallel to the light emitting layers.

This allows for multiple light emitting structures; i.e. OLED assembliesto be arranged between the substrate layers, and the light intensity ofthe output light is thus improved.

In embodiments, at least one of the first and the second substratelayers may be electrically conductive.

The substrate layer may itself be electrically conductive or it may beprovided with an electrode or an electrically conductive film.

Typically, the first substrate layer may be provided with a firstelectrode which is in electrical contact with the first electricallyconductive layer and the second substrate layer may be provided with asecond electrode which is in electrical contact with the secondelectrically conductive layer.

Accordingly, at least one anode and at least one cathode are formed onthe substrate layers.

In embodiments, at least one of the first and the second electrodes maybe patterned.

This allows for connecting multiple OLED assemblies in series such thatthe overall performance of the device is improved. Furthermore, thisallows for one or more of the individual OLED assemblies to be addressedseparately.

In alternative embodiments of the present invention, the device mayfurther comprise at least one diffusive layer arranged to diffuse atleast part of the light emitted by the light emitting layer.

The diffusive layer diffuses the light emitted by the light emittinglayer, and the light output from the first and/or the second substratelayer is thereby improved. As a result, the output light will behomogenous and diffuse.

The device may further comprise at least one light redirecting structurearranged to redirect at least part of the light emitted by the lightemitting layer in a direction towards the first or the second substratelayers.

The light redirecting structure allows for an increased redistributionof and an enhanced light output from at least one of the substratelayers.

In order to provide for the output of light having a desirablewavelength distribution, the organic light emitting device of theinvention may further comprise a wavelength converting element arrangedbetween the first OLED assembly and the second OLED assembly.

The wavelength converting element may be arranged between, and spacedapart from, the OLED assemblies allowing for a so called “remotephosphor” application. This arrangement allows for the light quality(unpleasant peak brightness, colour control) to be improved and thecolour may be controlled by varying the properties of the wavelengthconverting material(s). Furthermore, the use of a wavelength convertingelement that is not directly attached to the light source alleviates therequirements with respect to temperature and light flux that thewavelength converting material can withstand.

In embodiments, the device may further comprise a light guide arrangedto guide at least part of the light emitted by the first or the secondOLED assemblies into the wavelength converting element.

The light guide serves to guide the light to the wavelength convertingelement and to capture and recycle light from the wavelength convertingelement(s).

An organic light emitting device of the present invention may be used ine.g. decorative lighting, shop lighting and lighting for atmospherecreation and is suitable for large area applications.

These and other aspects of the invention will be apparent from andelucidated with reference to the embodiment(s) described hereinafter.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a vertical sectional view of an organic light emitting deviceaccording to one embodiment of the present invention.

FIG. 2 is a top-view of the organic light emitting device in FIG. 1.

FIGS. 3 a-c show examples of an organic light emitting device accordingto embodiments of the invention, wherein at least part of at least onesubstrate layer is reflective.

FIGS. 4 a-d illustrate various configurations of the OLED assemblies ofan organic light emitting device of the invention.

FIG. 5 a-f illustrate alternative embodiments of the invention, whereinthe light emission from each of the OLED assemblies are directed indifferent directions.

FIGS. 6 a-c show top-views of exemplary OLED assembly configurations ofembodiments of the present invention.

FIG. 7 illustrates an embodiment of the invention, wherein the first andthe second electrically conductive layers are in electrical contact withthe first and the second electrically conductive layers, respectively.

FIGS. 8 a-d illustrate exemplary embodiments of the invention, whereinat least one of the first and said second substrate layers is patterned.

FIG. 9 illustrates an embodiment of an organic light emitting device ofinvention comprising at least one diffusive layer.

FIG. 10 illustrates an embodiment of an organic light emitting device ofthe invention comprising at least one reflective layer.

FIG. 11 illustrates an embodiment of an organic light emitting device ofthe invention comprising at least one beam splitter.

FIG. 12 illustrates another embodiment of the invention, wherein theorganic light emitting device comprises a wavelength converting elementand a light guide.

DESCRIPTION OF A PREFERRED EMBODIMENT OF THE PRESENT INVENTION

One embodiment of an organic light emitting device 100 according to thepresent invention is illustrated in FIG. 1, and comprises a firstsubstrate layer 101 and a second substrate layer 102. The device furthercomprises at least a first OLED assembly 103 and a second 104 OLEDassembly arranged between the first 101 and the second 102 substratelayers. Each of the first 103 and second 104 OLED assemblies comprises afirst electrically conductive layer 105, a second electricallyconductive layer 106 and an organic light emitting layer 107 arrangedbetween the first 105 and the second 106 electrically conductive layers.

In FIG. 1, the first 105 and second 106 electrically conductive layersand organic light emitting layer 107 are shown only for the first OLEDassembly 103, although the second OLED assembly 104 has the samestructure.

Each of the first 103 and the second 104 OLED assemblies is arranged toform a non-zero angle in relation to at least one of the first 101 andthe second 102 substrate layers, respectively.

Here, the OLED assemblies 103 and 104 are arranged perpendicular to thesubstrate layers 101 and 102.

When a voltage is applied, current starts flowing through the device100. Current flows from the first electrically conductive layer 105 tothe second electrically conductive layer 106. Accordingly, negativelycharged electrons move from the second electrically conductive layer 106into the light emitting layer 107. At the same time, positive charges,typically referred to as holes, move from the first electricallyconductive layer 105 into the light emitting layer 107. When thepositive and negative charges meet, they recombine and produce photons(light).

In this embodiment, the first electrically conductive layer 105 servesas an anode layer, and the second electrically conductive layer 106serves as a cathode layer. However, the first electrically conductivelayer 105 may serve as the cathode, and the second electricallyconductive layer 106 as the anode.

At least one of the electrically conductive layers 105 and 106 istransparent to the photons generated, and light will be emitted from oneOLED assembly towards another.

Typically, the first and the second OLED assemblies may be arranged at adistanced from each other. This distance may be varied depending on theapplication and desired light effect to be achieved.

Light emitted from at least one of the OLED assemblies 103 and 104 ismixed in the region defined between the OLEDs and is emitted eitherthrough the first substrate layer 101 or the second substrate layer 102,or both.

Hence, at least one of the first and the second substrate layers 101 and102 may be transparent, i.e. comprise a material with a good opticaltransmittance.

Accordingly, light may be emitted from either a single surface or fromseveral surfaces, thereby enhancing the total light intensity of theOLED device. It is also possible to obtain various ratios of lightemission from different surfaces.

As is illustrated in FIG. 2, in a device 200 of the invention, light maybe emitted from both the first 201 and the second 202 substrate layersas well as in a lateral direction; i.e. a direction perpendicular to thelight emitted from the substrate layers 201 and 202.

The length of the substrate layers 201 and 202, and hence the length, l,of the OLED device 200 depends on the desired application and may be inthe range of from 10 cm up to a few meters.

The length of the OLED assembly; i.e. the distance between the first 201and the second 202 substrate layers may be in the range of from 1 to 20cm, e.g. 5 to 15 cm.

The ratio of the OLED assembly length to the distance, d, between theindividual OLED assemblies is typically above 1, e.g. from 2 to 5. Theratio of the OLED 110 assembly length to the distance, d, is importantin determining the intensity of the light as well as determining theangular range of light transmitted through such an assembly.

At least a part of at least one of the first and said second substratelayers 101 and 102 may be reflective, as is illustrated in FIG. 3.

This allows for the light emission to be directed and controlleddepending on the desired light effect and application.

In situations where a less transparent high intensity light emittingdevice is desired, the second substrate layer 102 may be transparent;and the first substrate layer 101 may be provided with a reflectivematerial 301, which is still partly transparent, e.g. 50% transmissiveor reflective in a specific part of the visible range (FIG. 3 a). Thisway, the light emission from the device is optimized in one direction.

In embodiments, the second substrate layer 102 may be transparent andthe first substrate layer 101 may comprise reflective parts 301 andtransmissive parts 302 (FIG. 3 b). Alternatively, the first and secondsubstrate layers 101 and 102 may comprise reflective parts 301 andtransmissive parts 302 (FIG. 3 c).

Accordingly, the light emission may be directed and varied depending onthe application and desired transparency.

As mentioned, the first and the second OLED assemblies should bearranged to form a non-zero angle in relation to at least one of thefirst and the second substrate layers.

Typically, each of the first and the second OLED assemblies may bearranged to form an angle which is larger than 30° in relation to atleast one of the first and the second substrate layers. Such anarrangement is illustrated in FIG. 4, where the OLED assemblies 403 and404 are non-perpendicularly aligned to the substrate layers 401 and 402.

In this arrangement, the direction of the emitted light may be adjustedwith respect to the substrate layer(s). Furthermore, the transmissionangle with respect to the substrate layers 401 and 402 may becontrolled.

For example, if the maximum emission angle from the device issubstantially different from the maximum transmission angle, one maylook through the device in the on-state without getting blinded by thehigh light intensity. Alternatively, such an arrangement allows lightfrom external sources, such as daylight to enter only under controlleddirections, while being able to emit a controlled amount of light inother controlled directions. Accordingly, both external light sourcesand device related light sources are effectively integrated.

In preferred embodiments, illustrated in FIG. 5, the OLED assemblies 503and 504 are arranged to form an angle of 90° in relation to thesubstrate layers 501 and 502.

Accordingly, the light emitting layers 507 and 507′ of the first OLED503, and the second OLED 504, respectively, are arranged to face eachother and light will be emitted parallel to the light emitting layer507.

In such embodiments, it is possible to stack several OLED assembliesperpendicular to the substrate layers, and achieve a higher lightintensity per unit area.

The light emission from the OLED assemblies 503 and 504 may becontrolled and directed in different directions. For example, both thefirst and the second electrically conductive layers 505 and 506 may betransparent to the light generated (FIG. 5 a).

Alternatively, only one of the first and the second electricallyconductive layers 505 and 506 may be arranged to emit light, i.e. theOLED assemblies 503 and 504 are single side emitting elements. Thus,light may be emitted in the same direction (FIG. 5 b) or in oppositedirections (FIG. 5 c). Hence, only one of the electrically conductivelayers 505 and 506 is transparent to the light generated.

In embodiments, both a completely transparent OLED assembly 503(comprising transparent electrically conductive layers) and a singleside emitting OLED assembly 504 may be used (FIG. 5 d).

Alternatively, as is illustrated in FIG. 5 e multi-coloured emittingOLED assemblies 503 and 504 may be used. Various colour effects may thusbe achieved.

Furthermore, it is possible to use pixelated OLED devices 503 and 504 inorder to display information such as text, pictures or even movies (FIG.5 f).

FIG. 6 illustrates a top-view of exemplary configurations of the OLEDassemblies arranged perpendicularly to the substrate layer (FIG. 6 b)and non-perpendicularly (FIGS. 6 a and c).

Typically, at least one of the first and the second substrate layers iselectrically conductive.

Accordingly, one of the substrate layers may itself be electricallyconductive or may be provided with an electrode, e.g. an electricallyconductive film,

According to one exemplary embodiment, as shown in FIG. 7, the firstsubstrate layer 701 is provided with a first electrode 702 which is inelectrical contact with the first electrically conductive layer 703 andthe second substrate layer 704 is provided with a second electrode 705which is in electrical contact with the second electrically conductivelayer 706.

Examples of electrode materials (or substrate materials when thesubstrate itself is electrically conductive) include e.g. indium tinoxide (ITO), tin oxide (e.g. doped with fluor or antimony), zinc oxide(e.g. doped with aluminium), poly-ethylenedioxythiophene (PEDOT), indiumzinc oxide, stacks of several electrically conductive metals. A numberof materials and combinations of materials may be used and these areknown to those skilled in the art.

Accordingly, the substrate layers 701 and 704 form at least one anodeand at least one cathode.

In embodiments, anodes and cathodes may be alternated on each substratelayer such that consecutive devices may be connected in series. Thus,much lower currents need to be transported over the substrate contactlines.

In embodiments of the invention, illustrated in FIG. 8, at least one ofthe first and the second electrodes 801 and 802 is patterned.

Either one of the electrodes may be patterned (FIG. 8 a) such that eachOLED assembly may be adressed separately, or both electrodes may bepatterned (FIG. 8 b). In the latter case, more than one OLED assemblymay be adressed separately. Alternatively, the first substrate layer iscovered with both an an anode and a cathode (FIG. 8 c).

In FIG. 8 d, the electrodes are patterned in such a way that the OLEDsare connected in series.

The OILED assemblies may be driven with either DC or AC current.

Referring now to FIG. 9, an exemplary embodiment of a light emittingdevice 900 according to the invention is illustrated.

In this embodiment the device 900 comprises at least one diffusive layer903 arranged to diffuse at least part of the light emitted by the lightemitting layer.

Such a diffusive layer 903 may be arranged on the first 901 or thesecond 902 OLED assemblies, or on both.

The diffusive layer 903 diffuses the light emitted by the light emittinglayer, and serves to increase the light extraction such that theemission of light parallel to the light emitting layer is enhanced.

The diffusive layer 903 may also comprise a reflective material whichserves to redirect the light emitted in angles non-parallel to the lightemitting layer.

A diffusive layer 903 may be arranged to receive light from the firstelectrically conductive layer of the OLED assembly 901, or alternativelyfrom the second electrically conductive layer.

In embodiments, the device 1000 comprises at least one light redirectingstructure arranged to redirect at least part of the light emitted by thelight emitting layer in a direction towards the first or the secondsubstrate layers 1004 and 1005 (FIG. 10).

The redirecting structure may be a reflective layer 1003. Such areflective layer 1003 may be diffuse reflective, specular reflective orangle dependent reflective. For example the reflective layer 1003 maycomprise surface relief patterns; i.e. have a segmented reflectivestructure as is illustrated in FIG. 10.

The reflective layer 1003 allows for an increased redistribution oflight and an enhanced light output from at least one of the substratelayers 1004 and 1005.

Instead of, or in addition to, a reflective layer, the device maycomprise a beam splitter 1103 (FIG. 11) which serves the same functionas the reflective layer; i.e. to redirect the light and enhance thelight output from the substrate layers 1104 and 1105.

In order to enhance the decorative light effects and to provide for theoutput of light having a desirable wavelength distribution, the organiclight emitting device 1200 of the invention may further comprise atleast one wavelength converting element 1201 arranged between the firstOLED assembly 1202 and the second OLED assembly 1203.

As used herein the term “wavelength converting element” refers to anelement that absorbs light of a first wavelength resulting in theemission of light of a second, longer wavelength. Upon absorption oflight, electrons in the material become excited to a higher energylevel. Upon relaxation back from the higher energy levels, the excessenergy is released from the material in form of light having a longerwavelength than of that absorbed. Hence, the term relates to bothfluorescent and phosphorescent wavelength conversion.

The wavelength converting element 1201 is arranged between, andtypically spaced apart from, the OLED assemblies 1201 and 1202 allowingfor a so called “remote phosphor” application. In traditional lightemitting devices. the wavelength converting material, i.e. the phosphoris embedded in glue that is directly attached to the light source or theLED chip. The use of wavelength converting material that is not directlyattached to the light source alleviates the requirements with respect totemperature and light flux that the wavelength converting material canwithstand. Therefore, this so-called remote phosphor embodiment allowsfor a low colour temperature and a good colour rendering index.Furthermore, the light quality (unpleasant peak brightness, colourcontrol) may be improved and the colour may be controlled by varying theproperties of the wavelength converting material(s). Furthermore, aluminaire manufacturer can choose the colour independently of theLED(s).

In embodiments, the device 1200 further comprises a light guide 1204arranged to guide at least part of the light emitted by the first or thesecond OLED assemblies 1202 and 1203 into the wavelength convertingelement 1203.

The light guide 1204 also serves to guide the light from the wavelengthconverting element 1201 and concentrate it to the edges of the element1201. This allows for an increased intensity of light emitted from thesubstrate layers 1205 and 1206.

The organic light emitting device of the present invention may furthercomprise additional optical components. Such additional components maye.g. be diffusive or reflective layers arranged on top of at least oneof the substrate layers; i.e. arranged on the light output surface ofthe substrate layer(s). Such additional components may be used toenhance the decorative light effect.

In addition to the various configurations described above it is alsopossible to place additional transparent OLED assemblies at the bottomand even at the sides of the stack in order to increase the intensityand obtain various decorative effects.

An organic light emitting device according to the invention may be usedin several applications, e.g. decorative lighting, shop lighting andlighting for atmosphere creation.

In another aspect, the present invention relates to a light sensordevice comprising an organic light emitting device as describedhereinbefore.

Such a light sensor device may comprise a control unit, a light sensoran organic light emitting device of the invention. The control unit canbe adapted to perform at least one measurement using the light sensorand to control the intensity of the light emitted by the individual OLEDelements based on the at least one measurement.

The light sensor may either be positioned within the organic lightemitting device or outside as an external device connected to the devicevia a connector, such as a connecting wire.

It is also possible to connect other type of sensing means to the deviceof the invention, e.g. to measure the presence and/or actions of peoplein an environment and adapt the lighting according to the actionsmeasured.

It is also possible to control the light emitted by the individual EDassemblies based on the day or time.

While the invention has been illustrated and described in detail in thedrawings and foregoing description, such illustration and descriptionare to be considered illustrative or exemplary and not restrictive; theinvention is not limited to the disclosed embodiments.

Other variations to the disclosed embodiments can be understood andeffected by those skilled in the art in practicing the claimedinvention, from a study of the drawings, the disclosure, and theappended claims. For example, depending on the OLED assemblies, OLEDelement configuration, additional optical components and substratelayers used, various organic light emitting devices may be obtained. Theinvention is not limited to a specific organic light emittingcomposition or a specific wavelength converting material.

1. An organic light emitting (OLED) device comprising a first substratelayer and a second substrate layer, at least one of said first and saidsecond substrate layers being electrically conductive at least a firstOLED assembly and a second OLED assembly arranged between en said firstand said second substrate layers; wherein each of said first and secondOLED assemblies comprises a first electrically conductive layer, asecond electrically conductive layer and an organic light emitting layerarranged between said first and said second electrically conductivelayers; and wherein each of said first and said second OLED assembliesis arranged to form a non-zero angle in relation to at least one of saidfirst and said second substrate layers.
 2. An organic light emittingdevice according to claim 1, wherein at least one of said first and saidsecond substrate layers is transparent.
 3. An organic light emittingdevice according to claim 1 wherein each of said first and said secondOLED assemblies is arranged to form an angle which is larger than 30° inrelation to at least one of said first and said second substrate layers.4. An organic light emitting device according to claim 3, wherein eachof said first and said second OLED assembly is arranged to form an angleof 90° in relation to at least one of said first and said secondsubstrate layers.
 5. An organic light emitting device according to claim1, wherein said first substrate layer is provided with a first electrodein electrical contact with said first electrically conductive layer andwherein said second substrate layer is provided with a second electrodewhich is in electrical contact with said second electrically conductivelayer.
 6. An organic light emitting device according to claim 5, whereinat least one of said first and said second electrodes is patterned. 7.An organic light emitting device according to claim 1, furthercomprising at least one diffusive layer arranged to diffuse at leastpart of the light emitted by said light emitting layer.
 8. An organiclight emitting device according to claim 1, further comprising at leastone light redirecting structure arranged to redirect at least part ofthe light emitted by said light emitting layer in a direction towardssaid first or said second substrate layer.
 9. An organic light emittingdevice according to claim 1, further comprising a wavelength convertingelement arranged between said first OLED assembly and said second OLEDassembly.
 10. An organic light emitting device according to claim 9,further comprising a light guide arranged to guide at least part of thelight emitted by said first or said second OLED assembly into saidwavelength converting element.